Since a hydrogel contains water as a medium, it is useful as a gel having high biocompatibility and is used in various fields including applications for commodities such as a paper diaper, cosmetics, and fragrances.
Examples of a conventional hydrogel may include a polymer gel formed by cross-linking a polymer chain to form a three-dimensional net structure, and forming a non-covalent bond between the structure and a medium such as water to swell the structure. For a natural polymer gel formed from a polysaccharide such as an agarose or a protein, and a synthetic polymer gel in which polymer chains are cross-linked through a chemical covalent bond, such as an acrylamide gel, many researches of physical properties and application developments of the polymer gel have been carried out.
In recent years, in addition to the gels formed from the polymers described above, a hydrogel formed by self-assembly of an organic compound having relatively low molecular weight has been found, and widely studied.
Most of the low molecular weight gelators that have been proposed are amphipathic compounds having a long chain alkyl group as a hydrophobic moiety in combination with a hydrophilic moiety. Examples thereof may include an amphipathic compound in which the hydrophilic moiety is amino acid (Non-Patent Document 1), an amphipathic compound in which the hydrophilic moiety is peptide (Patent Documents 1 and 2), an amphipathic compound in which the hydrophilic moiety is saccharide (Non-Patent Documents 2 and 3), and an amphipathic compound in which the hydrophilic moiety is polyol (Non-Patent Document 4). In addition, a low molecular weight gelator utilizing a property in which a peptide consisting of valine easily forms a β-sheet structure is also proposed (Non-Patent Document 5).
Using such a low molecular weight hydrogelator, a hydrogel can be formed by stirring the hydrogelator and water as a medium with heating under a temperature condition of about 100° C., dissolving and dispersing the gelator in water, and then allowing the solution to stand at room temperature.